Many modern vehicles are equipped with reactive passenger restraints such as airbags, seatbelt tensioners, or other reactive restraints that are activated in an event of a collision to mitigate injury to occupants. To control deployment or activation of such reactive restraints, various types of occupancy sensors are typically installed in vehicles. For example, weight or pressure sensors are incorporated into seats to detect whether or not an occupant is present in a particular seat. In another example, various types of transducers, such as ultrasonic sensors, microwave sensors, active infrared rangefinders, and capacitive proximity sensors, have been proposed as refinements over weight sensors. Such transducers are typically required to be installed in large numbers (e.g., three to four per each occupant seat), at multiple locations, and in combination with various other types of sensors in order to detect some positional information of occupants.
However, such conventional occupancy sensors, even when many of them are used in combination, are still prone to false or failed detections, since they are easily tricked by non-human objects or are sensitive to ambient conditions such as humidity. Furthermore, such conventional occupancy sensors cannot provide occupant-related information other than an indication of presence and some limited positional information. As emphasis on vehicle safety and automation continues to grow, more comprehensive and detailed occupant-related information may be needed to automate various vehicle components, provide comprehensive monitoring, or otherwise improve safety and comfort of drivers and occupants.